Infectious bronchitis virus (IBV) is a member of the genus coronavirus of the family Coronaviridae. The virus is usually about 80-100 nm in size, being round with projecting 20 nm spikes. IBV is the causative agent of an acute, highly contagious disease in chickens of all ages, affecting the respiratory, reproductive and renal systems.
IBV has been reported in all countries where an intensive poultry industry has been developed. Young chickens up to 4 weeks of age are most susceptible to respiratory disease, infection leading to high rates of morbidity and to mortality resulting from secondary bacterial infection. Infection in layers results in a drop in egg production, or failure to lay at full potential, together with an increase in the number of down-graded eggs with thin, misshapen, rough and soft-shells produced. Although layers usually recover from the disease, their egg production rarely returns to pre-infection levels. Thus infection of flocks of chickens with IBV can have a serious economic effect.
Spackman and Cameron (Veterinary Record, (1983), 113, 354-355) isolated IBV from pheasants with a history of respiratory signs and aberrant egg production. This disease problem in pheasants was successfully controlled by the use of oil-based inactivated IBV vaccine. Thus the term poultry, as used herein, is intended to embrace chickens, pheasants and any other domesticated bird serving as a source of eggs or meat and that are susceptible to infection by IBV.
The only practical means of preventing infectious bronchitis in poultry is to vaccinate against the infection. Two main types of vaccine are available and they are attenuated and inactivated.
One such known isolate is the Georgia 98 strain (GA-98), which was received from the University of Georgia Poultry Diagnostic and Research Center (PDRC) by Intervet, Inc., Millsboro, Del., U.S. Veterinary License No. 286 on Feb. 11, 2000. This strain has shown resilience to many of the commercially available IBV vaccines. Accordingly, the art field is in search of a vaccine for the GA-98 strain of IBV.